Merge from vendor: fix potential infinite loop in when executing -c command

[sobomax]

Summary

There is a serious issue in the current tcsh code which causes -c command to go into infinite loop. The original issue was reported here:

https://bugs.astron.com/view.php?id=113

And fixed here:

https://github.com/tcsh-org/tcsh/commit/83c5be028419b3f27c3cc707b88fb21bfa4e1b11

Test Plan

#include <assert.h>
#include <fcntl.h>
#include <signal.h>
#include <unistd.h>

int main(void)
{
  int devnull;

  assert(signal(SIGINT, SIG_IGN) != SIG_ERR);
  devnull = open("/dev/null", O_WRONLY);
  assert(devnull >= 0);
  assert(dup2(devnull, STDOUT_FILENO) >= 0);
  assert(close(devnull) == 0);
  execl("/bin/tcsh", "/bin/tcsh", "-c", "kill -TERM 99999", NULL);

  return (255);
}

[brooks]

I believe the correct way to handle this is to update the vendor tree and then merge. I'm happy to do that.

Is this only in the new version I imported on the 8th or do we need to MFC as well? If the latter, I suspect it makes sense to direct commit this patch to 12.1 rather than doing a full update this late in the release process.

[sobomax]

In D22099#482956, @brooks wrote:

I believe the correct way to handle this is to update the vendor tree and then merge. I'm happy to do that.

Is this only in the new version I imported on the 8th or do we need to MFC as well? If the latter, I suspect it makes sense to direct commit this patch to 12.1 rather than doing a full update this late in the release process.

Well, this affects anything since 11.2 at least onwards. I have not tested with 10.x, though. I suspect this specific fix would need to go into all currently supported releases. infinite_loop() implementation in one of two system shells in basic use-case scenario IS BAD, IMHO. You have a test code at hand BTW. :)

-Max

[sobomax]

Might need ("partial?") MFC into stable/11 stable/12.